1. Field of the Invention
The present invention relates to a hydraulic apparatus for adjusting the timing of the opening and closing of one or both engine valves, the intake valve and/or the exhaust valves of an engine using an actuator, according to the operating state of the engine.
2. Description of the Prior Art
Such hydraulic apparatuses for adjusting the timing of opening and closing of an engine valve are disclosed, as prior art, in JP7-139319A, JP7-139320A, JP8-28219A, JP8-121122A, JP9-60507A, JP9-60508A in which cam shafts are driven using a timing pulley synchronized with the engine crank shaft and a chain sprocket. A vane type valve timing mechanism which is arranged between the timing pulley and the cam shaft is driven by an actuator using a working oil provided from an oil pump through an oil control valve (hereinafter to be called "OCV"), so as to rotate the cam shaft relative to the crank shaft for advancing or retracting the cam shaft rotation relative to the crank shaft rotation. Thus, the timing of the opening or closing of the engine valve relative to the engine shaft rotation is shifted for the purpose of reducing exhaust gases and improving fuel efficiency.
A plunger in the actuator employed in such hydraulic apparatuses of the prior art is formed as a tapered pin, having an acute cone angle. Such a plunger is disclosed as a stopper pin, for example, in JP9-60508A.
In the hydraulic apparatuses having such a structure for adjusting the timing of the opening and closing of an engine valve in the prior art, a relatively large clearance is required between the tapered surface of the plunger and its engaging hole.
When the engine begins running from a state in which the engine is stopped with the plunger engaged with the hole, humming results in the engine. In turn this causes unpleasant noises. Additionally, when the tapered surface of the plunger is engaging with the hole, the engaging surface is inclined with respect to the rotation axis, and this causes a partial force urging the plunger in a direction of detachment. Thus, there is a tendency for the plunger to fall off.